Current rechargeable battery systems involve a charge cycle and discharge cycle. There is a need for thermal regulation or other current flow control measures that prevent too much current from being drawn from the unit energy cells, causing overheating of the energy interface and the individual cells. In addition, with reference to FIG. 1, there is a need for a cool-down period between charging the battery and its use (discharging the battery), as well as between use and when the battery can be charged again. Fast charging or discharging in particular can be especially prone to overheating the battery. Failure to accommodate the cool-down period can result in permanent damage to the battery cells or possible fire or explosion. The difficulty with this cycle is that it may be interrupted by user demand, requiring use of the battery when it is in the middle of charging, or when immediate charging for immediate use are desired. Any additional thermal discharge (heating) results in loss of energy and waste heat as opposed to charge. An illustrative case is electric vehicles, wherein a discharging period, as the foot pedal is pressed to apply power to the motor, is abruptly interrupted by a charging period when the driver releases the foot pedal and applies the brakes to initiate regenerative braking; only to then release the brake and press the pedal again to apply power to the motor and initiate discharging again, and so on.
In addition, current battery systems suffer from a difference in the charge levels of individual cells, or from any defect or problem with a single cell. The defect can be from localized chemical or mechanical failure or overheating, charge level difference, or a manufacturing defect. For example, when the charge of a single cell in an array of cells is lower than the rest of the cells in the array, the array can only charge to the level of the lowest cell in the array, in effect limiting the useful potential of the entire array to that of a single cell. FIG. 2 shows how the array or bank of batteries, three in this case, on discharge can only discharge the amount of charge in the lowest level cell in the array (cell 1). Cells 2 and 3, on discharge (right side of drawing figure) have unusable charge remaining because they are unable to continue to discharge once cell 1 has been depleted.
There are methods for conditioning the whole array, but these methods add discharge and charge cycles that involve complete discharge of the cells, which over time puts wear on the entire array, shortening its useful life. For these reasons there is a need for selective removal or replacement of a single cell or multiple cells.
There is also a problem with the versatility of existing battery systems. The battery packs come in different shapes and sizes and have different voltages, built to individual specifications that are not compatible with each other, even though internally many are based on the same unit cell battery. When these battery packs no longer hold useful charge, essentially reaching the end of their effective lives, they are discarded. The packs containing these batteries are frequently only suffering from the condition of one or two cells which if replaced would return the pack to serviceability. Replacing the defective cells could return the pack to useful service, in this way extending the useful life significantly. In addition, the less effective cells of these packs can be used in less demanding applications that do not require their full capacity. Both of these solutions would extend the life of the battery systems and reduce the amount of waste significantly.
Current vehicle battery systems do not allow for the rapid change of the battery packs. This requires vehicles to utilize plug-in chargers. Charge for these systems takes several hours for the cool, charge, cool and discharge cycle. Users driving on longer trips than the effective range of the vehicle's battery pack, or that require immediate use in the middle of the charging cycle, place undue demand on the battery packs. This can lead to damage to the battery packs from overheating and potentially leading to fires.